Haven´t worked with lexan, but have worked with plexiglass and another material used in airplane windows (before lexan). Tape the area to be cut, with masking tape and use an old window pump sprayer to keep it moist, while cutting. Keeping it cool, during the cut, makes for much better results. Polishing the edges, will help reduce the starting points for cracks. Had a sheet of plexiglass, in the rear window of my SJ for years. Cleaning with a high pressure cleaner, works best. Don´t use a rag or papertowels, unless you have to, don´t rub it dry. If you have to use a cloth, rub only in one direction, circular rubbing will really mess with your night vision. A light tint, shows the scratches less. Waxing the plastic, helps remove some of the scratches, again in one direction.